Electric motor



A. BERTEA ELECTRIC MOTOR Nov. 9, 1948.

4 Sheets-Sheet 1 Filed March 7, 1945 INVENTOR.

A a m A ATTORNEY.

Nov. 9, 1948. A. BERTEA 2,453,358

ELECTRIC MOTOR Filed March 7, 1945 4 Sheets-Sheet 2 ALEX Beers/4,

INVENTOR.

1, I BY ATTORNEY.

A. BERTEA ELECTRIC MOTOR Nov. 9, 1948.

4 Sheets-Sheet 3 Filed March 7, 1945 Nov. 9, 1948.

A. BERTEA 2,453,358

ELECTRIC MOTOR Filed March 7, 1945 4 Sheets-Sheet 4 l I v 011. \9 Z 7 ALEX 615G754,

INVENTOR.

BY marz/ ATTORNEY.

Patented Nov. 9, 1948 UNITED STATES PATENT OFFICE ELECTRIC MOTOR Alex Bertea, Pasadena, Calif. Application March 7, 1945, Serial No. 581,420

' 4 Claims. (01; 172-36) My invention relates to electric motors and has particular reference to a novel field construction which permits the realization of greatly increased overall efiiciency over that which can be realized with conventional field constructions. The invention has particular utility when applied to small electric motors of the character used on aircraft.

In certain applications of small electric motors, it is necessary that the physical size and weight of the motor be kept to a minimum. A typical example of such an application is in the use of small electric motors on aircraft for the operation of fuel pumps, pumps for de-icing fluid and motors for operating cowl flaps, trim tabs and the like. In applications such as this, the realization of a high efliciency in a small electric motor is of considerable importance since it permits a smaller and lighter weight motor to be used to deliver the required amount of power. The improvement in efiiciency also results in a reduced system load with the result that a considerable saving may be effected in the size and weight of the batteries or generating equipment'used to supply power for the electrical system.

It is an object of my invention to provide an electric motor which has a substantially improved efiiciency through the use of a novel construction of the main field assembly.

It is also an object of my invention to improve the efilciency of an electric motor by reducing to a minimum the flux cancellation in the armature and by utilizing to the maximum advantage the repulsive and attractive forces between the armature poles and the field poles.

It is also an object of my invention to provide an electric motor of the character set forth in the preceding paragraphs which includes a novel field construction having pole face members which are serrated at their edges to provide a graduated repulsive and attractive effect, thereby permitting an increased pole face span.

It is an additional object of my invention to provide in a motor of the character set forth hereinbefore a novel field construction which includes an increased reluctance section in the center of the span of the field pole face to reduce to a minimum the flux cancellation in the armature.

In the manufacture and servicing of electric motors, a great deal of time is consumed in disassembling and assembling the motor. Assembly and disassembly operations are ordinarily complicated by the presence of lead wires which connect the brushes or brush holders with the main field requiring these wires to be disconnected before the brush carrying end bell can be separated from the remainder of the structure. Also dlfiiculty is often encountered in re-establishing the required alignment of the bearings which are mounted in the end bells.

It is, therefore, an additional object of the present invention to provide an electric motor which overcomes the above noted disadvantages by including a, novelmechanism for providing an electrical interconnection between the field windings and the brush holders.

It is also an object of my invention to provide in a motor of the character set forth in the preceding paragraph a novel field construction which greatly simplifies the operation of winding the field coils and which materially facilitates the assembly of the motor:

It is an additional object of my invention to provide an electric motor of the character described in which all of the lead wires are mounted in the brush holder end bell so that the end bell may be removed without requiring disconnection of wires or interconnecting leads.

Other objects and advantages of my invention will become apparent from a study of the following specifications, read in connection with the accompanying drawings, wherein:

Fig. 1 is a side elevational view of a small electric motor constructed in accordance with the preferred embodiment of my invention;

Fig. 2 is an end elevational view of the motor illustrated in Fig. 1;

Fig. 3 is a cross sectional view taken substantially along the line III-III of Fig. 1;

Fig. 4 is a longitudinal sectional view taken substantially along the lines IV-IV of Figs. 1 and 2;

Fig. 5 is an exploded plan view showing the two halves of the field structure separated prior to assembly;

Fig. 6 is a longitudinal sectional view through one of the field structure halves which are shown in Fig. 5;

Fig. 7 is a side elevational view illustrating the form of stampings used in assembling the field structure;

Fig. 8 is a fragmentary exploded perspective view showing the stacking arrangement used in laminating the field structure;

Fig. 9 is a fragmentary view taken as indicated by the line IXIX of Fig. 3 and showing the arrangement of teeth used on the peripheral edges of the pole faces;

3 Fig. is a cross sectional view taken substantially along the line 12-)! of Fig. i;

Fig. 11 is a fragmentary sectional view taken substantially along the line -121 of Fig. 10;

Fig. 12 is a fragmentary sectional view taken substantially along the line XII-XII of Fig. 10; and

Fig. 13 is a fragmentary sectional view taken substantially along the line XIIL-XIII of Fig. 4 and illustrating the construction of the front bearing retainer.

Referring to the drawings, I have illustrated in Fig. 1 the preferred embodiment of my invention as comprising an electric motor I which consists of a front end bell 2, a main housing 2 and a rear end bell 4. Between the bells 2 and 4 and within the housing 2 there is mo ted an armature 5 which is supported upon a shaft 6, one end 1 of which protrudes through the end bell 2 to permit connection to an apparatusto be operated by the motor. The end bell 4 preferably carries a suit-.- able terminal or plug 8 by means of which electric power may be conveyed to the motor and also mounts brush holders 8 and ill. The end bell 4 may carry a mounting foot I I and the forward end of the main frame 2 maybe provided with a pair of similar feet i2 and i3. This provides a threepoint support for the motor, allowing it to be firmly secured to any plane surface. To this end the feet H, II and I! are preferably bored and tapped as indicated at I4 in Fig. 4.

Within the main frame 2 there is mounted a field structure I! seen in cross section in Fig. 3 and in longitudinal section in Fig. 4. The field structure Ill is formed of separable halves i6 and I1 which, when assembled, define a field structure which completely encircles the armature 5 a ls=\ g machine, it being provides a pair of oppositely disposed pole faces II and is. About the halves i6 and i1 there are wound field coils and 2|. The halves l6 and ii are similar in shape and arrangement and are generally c-shaped. They comprise aplurality of laminations 22 which are formed as shown in Fig. 7 and stacked as indicated in Figs 8 and 9.

Each of the laminations 22 includes oppositely positioned arcuate pole face portions 22 and 24, the portion 22 being somewhat shorter than the portion 24. These pole face portions are joined by-leg portions 25 and 26 to a central portion 21, the sides of which are substantially parallel and disposed substantially at right angles to the leg portions 25 and 26. types and differ only in the length of the short arcuate pole face section 22. One set of laminations is formed with a relatively sharp pointed tooth portion 28 at the inner end of the arcuate portion 23 as shown by solid lines in Fig. 7. The alternate set of laminations differs in that the two portions are cut off along the dotted line 29 shown in Fig. 7.

The laminations are stacked as shown in Fig. 8.

The first lamination which is placed in the stack (22a in Fig. 8) may be of the type which is out along the line 30 of Fig. '7. This lamination is placed with the long pole face portion 24 at the top as viewed in Fig. 8. The next lamination (2222) may comprise a lamination out along the dotted line 29 in Fig. 7 but placed in reverse position so that the short pole face portion 23 is at the top. The third lamination (220) is identical with 220. and is placed with its long pole face portion 24 at the top as viewed in Fig. 8. The fourth lamination may comprise one of the type shown in Fig. 7 as having a sharp inner corner 28 but is placed in reverse position so that the sharp pointed The laminations 22 are of twostacked with the short pole face portion 28 and the short arcuate pole face portion 22 are at the top as shown in Fig. 8. The fifth lamination is theisame as the first andthe sixth is the same as the second, andso forth.

When this arrangement of laminations is employed. the portions of the pole faces adiacent each other (i. e., nearest the field windings 2| or 2 I) present a toothed or serrated aspect as is illustrated in Fig. .9 comprising long teeth 22 (so identified because they are defined by the pointed portions 28 of the laminations) with teeth of intermediate length 29 defined by the portions out along the dotted line 29 of Fig. and positioned alternately with respect to the long toothed portions 22. Between each of the members 24 and 29 there are positioned laminations identified in Fig, 9 by the reference character 20, the portions 20 being defined by a straight inside surface II of the leg portion 2B of the lamination 22 shown in Fig. 7.

The laminations are stacked upon assembly dowels 22 which are passed through dowel receiving bores 22 and 34. When stacked, the laminations are secured to each other :by means or small rivets 35 which are passed through the complete stack.

The central parallel sided portions 21 of the stacked laminations define a parallel sided solid. upon which the field windings 20 or 2| are wound. The windings are insulated from the lamina-ti is 22 as by means of an inner layer 28 of insult... material and are preferably protected on the ontside by an exterior layer 21 of insulating material. The windings 20 and 2| are applied before the two field structure halves are Joined. By so doing the windings 20 and 2i may be put on by a coil wind:- only necessary to provide suitable supporting fixtures for rotating the U- shaped structure about an axis passing through the center of the central portion 21.

The alternate stacking of the laminations as previously described provides at the outer ends of the pole face portions a plurality of transversely extending fingers 3| which are spaced axially of each other by the thickness of a single lamination due to the intervening laminations which are portions 22 adjacent the long pole face portions 24. when. the two field structure halves l6 and II are to be assembled to form the completed field structure. they are placed opposite each other as show" i Fig. 5 with the fingers ll of one half positi opposite the space between adjacent fingers of the other half. The two halves are then moved to ward each other to the relative positions shown in Fig. 3. In this position the arcuate pole face portions 23 and 24 of both halves l6 and i1 lie on a circular cylinder which is slightly larger in diameter than the outside diameter of the arms-- ture 5.

It will be noted in Fig. 3 that the fingers iii defined by the long pole face portions 24 overlap as indicated by the solid line 38 and the dotted line 22- in Fig. 3. This overlapping portion has an arcuate width of approximately one-third the span between oppositely positioned short pole face portions 23. Thus the overlapping portion comprises a sec-tion which is axially continuous and which is flanked on either side by sections which consist of an alternate arrangement of laminations and air spaces the thickness of a single lamination. This, there is provided in the center of each field pole at low reluctance section flanked on either side by a section of somewhat higher reluctance and of limited arcuate length.

In devising the field structure just described, recognition has been given to the fact that the forces producing a torque tending to rotate the armature are due principally to magnetic attraction and repulsion between, respectively, unlike and like armature and field poles rather than due to the effect of a current flowing in an armature conductor which is situated in a magnetic field. Recognition is also given to the fact that the armature poles of greatest strength are those which are in line with the brushes; that is, positioned midway between opposite field pole faces. It is therefore'desirable to extend the arcuate span of the field pole face to as close a proximity as is possible with the strongest armature pole. This is done in the above described nstruction by the tooth portions 28 and 28 descri din connection with Fig. 9. The tooth construction is employed in preference to extending the entire pole face as by so doing it is possible to avoid impairing the accommodation of armature poles that are spread farther apart since there is provided at the shorter teeth 2! and at the still shorter portions 30 additional rows of field pole heels. This permits utilization to the greatest extent of the maximum armature pole strength and also serves to blend out and reduce to a minimum the torque unbalance produced by the enter- I ing of an armature pole face under the heel of the field pole. There is thus produced a torque smoothing efiect similar to that which may be obtained by the employment of skewed armature slots while avoiding the reduction in eifectiv armature winding space which accompanies a s ewing of the armature construction. The teeth also maintain a substantially constant attractive and repulsive force between the entering armature pole and the leaving armature pole, respectively, thus exerting a maximum torque over a maximum arcuate span.

The overlapping central portion "-39 and the higher reluctance portions which extend axially along either side of the central portion function to reduce to a minimum the short circuiting efiect provided by the conventional solid pole face construction as regards the magnetic path between adjacent armature poles which are positioned at right angles to the brush axis. The pole face thus operates in. part as though the poles were magnetically separate, avoiding a back attraction as the armature magnetic polarity reverses and affording a maximum repulsive effect as soon as the armature polarity hasbeen reversed.

By winding the field windings 20 and II directly upon the field structure instead of merely around the field pole piece as is the conventional form of construction, there is obtained a considerable increase in the efllciency of the field winding itself. With the form of winding described, the length of the non-working end turns are reduced to a negligible fraction of the entire winding length, whereas in. conventional constructions the major portion of the winding is used in the end connections.

The main frame 3 is of tubular form to receive the field structure I! and is by preference provided with an elliptical or oval cross section, as is best shown in Fig. 3, to make the most economical use of the space within which the laterally elongated field structure it is placed. The abutting end of the end bell 4 is shaped to conform to the shape of the main frame 3 and a shouldered lap joint, as is indicated at 40 in Fig. 4, maintains the required alignment between the end bell 4 and the main frame 3. The main frame I is 6 closed at its forward end by a radially extending portion 4i which is in turn bored as shown at I! to receive a boss 43 formed on the front end bell i. The end bell 2 is counterbored as indicated at 44 to receive a suitable anti-friction bearing 45 shown as comprising a ball bearing within which is rotatably supported the armature shaft I.- The bearing 4' is by preference slipped into the counterbore 44 while the shaft end I fits the inner race 1 of the bearing 45 with a press fit. The'bearing 4| is frictionally held in the counterbore 44 by means of a polygonal spring retainer 44 shown in detail in Fig. 13. The retainer 46 may be formed of a strip of fiat spring material such as spring brass or phosphor bronze. The counterbore 44 is made enough larger than the outside diameter of the" bearing 45 to permit the bearing 45 and the spring retainer 46 to both be placed within the counterbore 44. In placing the bearing 45 in the counterbore and within the retainer, the latter is deformed from its normal polygonal shape to a substantially circular shape, its resilient tendency to restore to the polygonal shape serving to fri'c-' tionally grip the outer race of the bearing 45 and hold the same within the counter bore in the end bell 2.

The shaft 4 is radially shouldered as indicated at 41 to limit endwise movement of the shaft 4 to the left as viewed in Fig. 4. Similarly, at the extreme right-hand end of the shaft 8, there is provided a reduced diameter portion 48 forming a shoulder 49. Upon the reduced diameter portion 48 there is pressed an anti-friction bearing 50 to engage the shoulder 49 and limit endwise movement of the shaft 8 to the right as viewed in Fig. 4. The outer race of the bearing 50 is slidably received within a counterbore 5| formed in an internal boss 52 carried by the end hell 4. The bore Ii is extended at a reduced diameter as shown at 53 completely through the end bell 4 to provide an interior space for accommodating electrical connections. The boss 52 is axially slotted as indicated at 55 to divide the boss 52 into a plurality of fingers which, by virtue of the resilience of the metal and the fact that the counterbore ii is provided with a normal diameter less than the outside diameter of the bearing 50, serve to provide a spring gripping action, by means of which the bearing is removably retained within the counterbore 5i. I

The interior space 54 accommodates electrical connections which may comprise electric wires 58' and I! which are suitably secured as by soldering to a pair of terminal pins 58 and 59 which are mounted in an insulating support Bil carried by the connector 8. The connector 8 may be secured to the end hell 4 as by means of a plurality of screws or rivets ii. The electric wires 56 and, 51 are passed through the slot and connected in a manner to be described hereinafter. The end bell 4 serves to also support the brush holders 9 and III. This support is provided by a pair of bosses 62 and 63 (Figs. 10 and 12) which are transversely bored as indicated at 64 to'receive a cup-like brush holder 6! formed of insulating material. The holder 65 is locked in'th'e bore 4 as by meansof a set screw 66. The insulator i5 is provided with an inner bore 61 within which is fitted a tubular contact member 68. The contact member 68 is bored as at 69 to receive a brush 10 formed of carbon or other suitable brush material. The brush it is urged inwardly toward the shaft 6 as by means of a compressionspring ll enclosed within the bore 69 and bearing at one end against the end of the brush II and at the other and against the bottom of the hole 81 in the insulator 85. The innermost end of the contact member 88 is provided with a pair of annular grooves II and ll of semi-circular cross section which serve to receive spring clip terminal such as are shown at 14 and I! in Fig. 10. The terminal 15 is connected to the previously mentioned conductor 58 while the clip 14 is secured to a field supply conductor 16. The conductor 18 is connected to a contact member Ill.

The assembly to be described employs four such contact members identified in Fig. 10 by the reference characters 11, 18, I8 and 88. These contact members are identical and are constructed as shown in Fig. 11. As is shown therein, the end bell boss 83 is bored as indicated at 8| to slidably receive an insulating member 82. The insulating member carries a metallic contact member 83 to which the conductor 51 is electrically connected as by being passed through a small transversely extending bore 84 and being soldered or otherwise suitably secured therein. A compression. spring 85 interposed between the insulator 82 and the bottom of the bore 8| resiliently urges the metallic member 83 into contact with a corresponding field terminal member as. The field terminal membars are mounted upon the field structure halves l8 and I! in positions to engage the contacting members "-80 when the motor is assembled as shown in Fig. 4. The terminal members 88 are mounted in insulating caps 8'? which are placed over the ends of the field windings 2i! and M as is shown in Figs. 5 and 6. The terminal members I! are pressed into a suitable bore 88 formed in the caps 81 and are themselves transversely bored as indicated at 89 to receive the end of a field winding conductor 80. The conductor 90 may be secured in the pin as by soldering or as by deforming the end of the pin so as to securely clamp the wire within the bore 89. Two oi the terminal pins are provided for each of the coils 2d and M, the terminals being connected to opposite ends of each coil.

When the field structure is assembled within the main frame 3 and the end bell is placed in position as is shown in Fig. 4, the electrical circuit of the motor is completed to place the two field windings in. series with the armature across the input terminals 58 and St. The additional elec- 'trical connections include a conductor 9% extended between the field terminal connectors l8 and 88 and the aforementioned conductor 5'! which is connected to the field terminal connector 18.

It will be noted that all. of these interconnections are between structures mounted within the end bell 4 so that removal oi the end bell d is permitted without requiring any of the electrical connections to be disturbed. This operation is permitted by employing the spring connectors H to join the field structures electrically to the brushes and terminals mounted in the and bell 4.

The assembly dowels 32 previously mentioned in the description of the field structure serve also to rotate the field structure within the motor frame when the motor is assembled. The dowels are all identical and consist of a length of cylindrical rod terminated at each end by smaller diameter portions 92 and tilt. These smaller diameter portions are received in suitable pockets 84 and 85 formed in bosses on the front end of the main. frame 3 and in the end hell 4., These pockets are so positioned that when the reduced diameter portions 92 and 83 are received therein, the field structure halves it and it will be spaced from each other the proper distance to define a circular bore within which the armature may rotate. Also the length of the dowels 82 between the shoulders adiacent the reduced diameter portions is adjusted to hold the main frame 3 and the end bell 4 in the proper spaced relation.

The armature is preferably constructed as shown. in Fig. 4 and comprises a series of laminations 88 which are stacked on the shaft 8 and held in place by means of collars 81 and 88 placed on the shaft. The rear end of the shaft mounts a commutator 88 which is connected in a conventional manner to armature windings I88 (Fig. 3) disposed within triangular armature slots defined by the star-shaped armature laminations 86.

In assembling the motor, the field structure is placed within the main frame I with the assembly dowels engaging the pockets 9!. 'The armature is installed with the front end bearing 4i placed within the counterbore 44. The rear end bell 4 is then slipped into place with the assembly dowels being received within the pockets 84. When the parts are thus assembled, they are held together by means of four longitudinally extending screws I! which are recessed within the end bell I and passed through suitable apertures provided in the field structure halves l6 and I1 and threaded into bosses formed in the end bell 4. With this construction the entire motor may be disassembled by removing the four screws i0! and reversing the assembly procedure. The field structure after removal may be divided into halves as is shown in Fig. 5 and the field circuits may be independently checked and rewound with ease if rewinding is required. Upon reassembly, the parts can go together only in oneway and when they are assembled in that fashion, they are automatically positioned in their required locations.

From the foregoing it will be observed that I have provided an electric motor construction which is characterized by the employment of a new and novel type of field structure. Attention is directed particularly to the teeth or serrations which are formed on the peripheral edges or the field poles and also to the screened or increased reluctance at the center of the field poles, these improvements serving to provide a material increase in the overall efliciency of the motor. As an example, comparative efiiclency tests were made with a commercially obtained motor using, on the one hand, the conventional field structure with which the motor was factory equipped and, on the other hand, a field structure of the character described hereinbefore. In making the tests all test conditions were maintained constant, the sole difference between the two tests being the substitution of my improved field for the conventional field furnished with the motor. The tests showed that by substituting my new field for the commercial field raisedthe maximum efficiency from 47% at 81 watts input to 70% at Z2 watts input and 67% at 81 watts input, an increase in eiiiciency of nearly 50%.

Attention is directed also to the ease with which the motor of my invention is disassembled and re-assembled, and particularly to the manner in which the electrical connections are made to the field structure to facilitate initial manufacture and repair operations.

While I have shown and described the preferred embodiment of my invention, I do not desire to be limited to any of the details of construction shown or described herein, except as defined in the appended claims.

9 I claim:

1. In an electric motor, a field structure com-,

prising a first plurality of laminations having an asymmetrical C-shape, the legs of said C-shape terminating in arcuate portions of given lengths all lying on the surface of a circular cylinder, a second plurality of laminations having an asymmetrical C-shape, the legs of said C-shape termimating in arcuate portions of lengths different from the given lengths of the first plurality and all lying on the surface of said circular cylinder, said first and second pluralities of laminations being arranged to define a plurality of circumferentially extending teeth spaced along the axial edges of said arcuate portions.

2. In an electric motor, a field structure comprising a pair of separable halves, each of said halves consisting of a plurality of stacked laminations having an asymmetrical C-shape with one of the legs of said C-shape longer than the other, said laminations ,beingalternately stacked with the long leg of one lamination placed upon the short leg of an adjacent lamination, the legs of said C-shape all terminating in arcuate portions lying on the surface of a circular cylinder, the long legged laminations of one of said halves being placed between the long legged laminations of the other of said halves to define an axially extending central pole face portion flanked on each side by a plurality of axially spaced and radially extending perforations.

3. In an electric motor, the combination of: a tubular main frame with end bells; an armature in said frame rotatably supported on said end bells; a field structure surrounding said armature, said field structure comprising a pair of separable halves each consisting of a plurality of stacked laminations, said laminations having an asymmetrical U-shape with one of the legs of said U-shape being longer than the other, said laminations being stacked alternately to provide a plurality of outwardly extending fingers immediately adjacent the armature and separated from each other by the thickness of the intervening lamination; and support means engaging one 10 of said end bells mounting said halves in said frame and normally supporting said halves with the outwardly extending fingers of one half disposed between the corresponding fingers of the other half.

4. In an electric motor, a field structure comprising a pair of separable halves, each of said halves consisting of a plurality of stacked laminations having an asymmetrical U-shape with one of the legs of said U-shape longer than the other, said laminations being alternately stacked with the long leg of one lamination placed upon the short leg of an adjacent lamination, the legs of said U-shape all terminating in arcuate portions lying on the surface of a circular cylinder, and means for interengaging said laminations and securing said stacked laminations to each other into a unitary structure.

ALEX BERTEA.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 451,574 Rice May 5, 1891 724,484 Meston Apr. 7, 1903 1,220,486 Amsler Mar. 27, 1917 1,314,132 Dorsey Aug. 25, 1919 1,424,164 Hoover Aug. 1, 1922 1,488,498 Hoff Apr. 1, 1924 1,495,827 Warren May 27, 1924 1,750,122 Oswald Mar. 11, 1930 2,158,145 Oster May 16, 1939 2,185,990 Schurch Jan. 2, 1940 2,230,008 Nowosielski Jan. 28, 1941 2,251,673 Gillen Aug. 5, 1941 2,274,480 Jepson Feb. 24, 1942 2,332,126 Allen Oct. 19, 1943 2,402,380 Dicke June 18, 1946 FOREIGN PATENTS Number Country Date 606,021 Germany Nov. 23, 1934 

